#!/bin/bash

echo

echo "\"0\" Å×½ºÆ®"
if [ 0 ]      # zero
then
  echo "0 Àº Âü."
else
  echo "0 Àº °ÅÁþ."
fi

echo

echo "\"NULL\" Å×½ºÆ®"
if [ ]        # NULL (empty condition)
then
  echo "NULL Àº Âü."
else
  echo "NULL Àº °ÅÁþ."
fi

echo

echo "\"xyz\" Å×½ºÆ®"
if [ xyz ]    # ¹®ÀÚ¿­
then
  echo "ÀÓÀÇÀÇ ¹®ÀÚ¿­Àº Âü."
else
  echo "ÀÓÀÇÀÇ ¹®ÀÚ¿­Àº °ÅÁþ."
fi

echo

echo "\"\$xyz\" Å×½ºÆ®"
if [ $xyz ]   # $xyz °¡ ³ÎÀÎÁö Å×½ºÆ®...
              # ÇÏÁö¸¸ ´ÜÁö ÃʱâÈ­µÇÁö ¾ÊÀº º¯¼öÀÏ ¶§¸¸.
then
  echo "ÃʱâÈ­ ¾È µÈ º¯¼ö´Â Âü."
else
  echo "ÃʱâÈ­ ¾È µÈ º¯¼ö´Â °ÅÁþ."
fi

echo

echo "\"-n \$xyz\" Å×½ºÆ®"
if [ -n "$xyz" ]            # Á» ´õ ¾î·Æ°Ô º¸ÀÌ°Ô.
then
  echo "ÃʱâÈ­ ¾È µÈ º¯¼ö´Â Âü."
else
  echo "ÃʱâÈ­ ¾È µÈ º¯¼ö´Â °ÅÁþ."
fi

echo

xyz=                        # ³Î °ªÀ¸·Î ÃʱâÈ­.

echo "\"-n \$xyz\" Å×½ºÆ®"
if [ -n "$xyz" ]
then
  echo "³Î º¯¼ö´Â Âü."
else
  echo "³Î º¯¼ö´Â °ÅÁþ."
fi


echo


# "false"°¡ ÂüÀÏ ¶§.

echo "\"false\" Å×½ºÆ®"
if [ "false" ]              #  "false"´Â ±×³É ¹®ÀÚ¿­ °°ÁÒ?
then
  echo "\"false\" ´Â Âü."   #+ ±×·¡¼­ ÂüÀÌ µÇ³×¿ä.
else
  echo "\"false\" ´Â °ÅÁþ."
fi

echo

echo "\"\$false\" Å×½ºÆ®"  # ÃʱâÈ­ ¾È µÈ º¯¼ö, ´Ù½Ã.
if [ "$false" ]
then
  echo "\"\$false\" ´Â Âü."
else
  echo "\"\$false\" ´Â °ÅÁþ."
fi                          # Èì, ÀÌ°Ô ¿ì¸®°¡ ¿øÇÏ´ø °ÅÁÒ.


echo

exit 0